Where does a motor make the most power, and should I run it there?

Peak power is at half free speed and half stall torque. For the default motor that is 471 W at 73.5 A and 53% efficiency. At 80% of free speed it still makes 302 W, 64% of the peak, on 30.6 A and at 82% efficiency.

Why does stall current matter if the motor never stalls?

It sets how many amps each newton-metre costs. Torque per amp is stall torque divided by stall current minus free current. A Kraken X60 in FOC mode gives about 0.0195 N·m per amp, so each 1 N·m takes about 51 A on top of the free current.

How much torque can a motor give continuously?

Far less than stall torque. Pololu’s rule for brushed gearmotors is to keep continuous load to about 20% to 30% of stall torque. Brushless motors are limited by winding temperature, so duty cycle matters more than any single number.

Can I use a motor that is not in the FRC list?

Yes. General mode takes any four endpoints, and FRC mode only adds presets. The straight-line model is exact for an ideal brushed motor and close for brushless ones. It ignores battery sag and heating.

Power transmission calculator

Motor Speed, Torque & Power Calculator

Read a DC motor’s torque, current, power, and efficiency at the speed your gearing puts it, from four datasheet numbers.

Input → stages → output

Edit any value and the drivetrain, target, and motor curves update immediately.

Calculator mode

Motor input

Use any motor’s published endpoint data

Motors

Voltage

Free speed

rpm

Stall torque

Free current

Stall current

Controller current cap

Not applied

Gear stages

14.6667:1 total

Efficiency / mesh

Stage 1

Driver

Driven

Stage 2

Driver

Driven

Motion target and results

Output speed

rpm

Output torque

Entered ratio: 14.6667:1
Predicted speed: 301.91 rpm
Speed vs. target: +0.6%
Efficient ratio: 14.811:1
Motor at target: 4,443.36 rpm · 39.1 A
Required power / motor: 362 W · 76.9% peak

Efficient point for the required power

Selected the higher-speed, lower-current point: 74.1% of free speed, 25.9% of stall torque, 77.2% modeled efficiency, and 39.1 A per motor.

Drivetrain and Custom motor performance

RPM and torque through each shaft, followed by the interpreted motor curves.

4,443.36 rpm · 39.1 A

Motor input

4,428.02 rpm

0.58 lbf·ft

12T → 48T

4:1

Shaft 1

1,107.01 rpm

2.25 lbf·ft

18T → 66T

3.667:1

Mechanism output

301.91 rpm

8 lbf·ft

Entered stages Efficient required-power solution Efficient continuous band 90%+ peak power · transient Low-speed stall risk Torque · 3 N·m stall Current · 145 A stall Power · 471 W modeled peak Efficiency · 87% modeled max

Most efficient solution for the required power

The movement needs 341 W at the output. With 94.1% drivetrain efficiency, each motor must deliver 362 W at its shaft. The calculator selects the higher-efficiency of the two motor-curve points that produce this power.

Efficient solution

Motor speed: 4,443.36 rpm · 74.1%
Current per motor: 39.1 A
Motor efficiency: 77.2% · 89% of max
Required shaft power: 362 W · 76.9% peak
Ratio for desired speed: 14.811:1

Estimated electrical input at this point is 469 W per motor · 469 W total at nominal voltage. This is the steady-state power for the entered speed and torque; acceleration requires additional power.

The curves are an engineering estimate, not a thermal or controller simulation. A breaker rating is not a motor-current cap; brief current can exceed that rating before a time-dependent trip. Battery or supply sag, configured controller limits, commutation, temperature, friction, and manufacturing variation change real performance.

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Quick answer

How it works

A DC motor’s torque falls in a straight line from stall torque at zero rpm to zero at free speed, and current falls with it. Power peaks at half free speed, but efficiency peaks much nearer free speed, so the point with the most power is rarely where the motor should run.

How to use the calculator

1Copy the four endpoints from the datasheet at the voltage you run: free speed, free current, stall torque, stall current. The calculator does not rescale them for a different voltage.
2Set the motor count. Motors share the torque, so each sits higher on its own curve.
3Enter your target and gear stages, then read where the target lands on the torque, current, power, and efficiency curves.
4Move that point toward free speed with a lower ratio, more motors, or less load until the current and efficiency are acceptable.

Key formulas

Motor speed & torque formulas

Torque at speed: T = T stall × (1 − n ÷ n free); Straight line from stall torque at 0 rpm to zero at free speed.
Current: I = I free + (I stall − I free) × T ÷ T stall
Power and efficiency: P = T × ω · η = P ÷ (V × I); ω is speed in rad/s. Peak power is ¼ × T stall × ω free, at half free speed.

Worked example

One motor or two on the same load

Inputs: The default 12 V motor (6,000 rpm free speed, 2 A free current, 3 N·m stall torque, 145 A stall current) drives the default 14.67:1 train at 97% per mesh. The load is 8 lbf·ft at 300 rpm.
Result: One motor: 39.5 A at 4,428 rpm, 77% efficient. Two motors: 20.7 A each at 5,214 rpm, 86% efficient, and the output speeds up to 356 rpm.

Each motor of the pair carries half the torque, so it runs faster and draws about half the current. Winding heat goes with current squared, so two motors at 20.7 A make about 55% of the heat of one at 39.5 A.

Common questions

What to know before using the result

Where does a motor make the most power, and should I run it there?: Peak power is at half free speed and half stall torque. For the default motor that is 471 W at 73.5 A and 53% efficiency. At 80% of free speed it still makes 302 W, 64% of the peak, on 30.6 A and at 82% efficiency.
Why does stall current matter if the motor never stalls?: It sets how many amps each newton-metre costs. Torque per amp is stall torque divided by stall current minus free current. A Kraken X60 in FOC mode gives about 0.0195 N·m per amp, so each 1 N·m takes about 51 A on top of the free current.
How much torque can a motor give continuously?: Far less than stall torque. Pololu’s rule for brushed gearmotors is to keep continuous load to about 20% to 30% of stall torque. Brushless motors are limited by winding temperature, so duty cycle matters more than any single number.
Can I use a motor that is not in the FRC list?: Yes. General mode takes any four endpoints, and FRC mode only adds presets. The straight-line model is exact for an ideal brushed motor and close for brushless ones. It ignores battery sag and heating.

Formula

F = ma + Fᵣ · T = Fr · P = Fv · GR = ∏(N driven ÷ N driver)

Output speed is motor speed divided by total ratio. Output torque is motor torque times ratio times efficiency. Linear targets use F = ma plus resistance at the wheel radius. Angular targets use τ = Iα plus resisting torque.

Engineering references

Assumptions and limits

Each row is one external mesh between a driver and a driven gear. Gears fixed to the same shaft turn together and add no mesh. Pitch, pressure angle, and center distance are not checked.
The motor is a straight line from free speed and free current to stall torque and stall current, at constant voltage. Battery sag, heating, and controller limits move the real curve.
Efficiency is one number per mesh, applied to every row. Bearing, windage, and lubricant losses are not included.
Acceleration targets assume constant acceleration from rest and no wheel slip. The motor is checked at the target speed with full acceleration torque, the hardest point of the run.

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